1. Technical Field of the Invention
The present invention relates to a gaseous component concentration determination apparatus and method for determining a concentration of a target component in a gas using laser beam.
2. Description of the Related Art
A concentration of a specific target component contained in a gas can be determined in the following manner.
Laser beam having an absorption wavelength λ1 unique to the target component is emitted from a laser emitter to the remotely-located gas. Scattered light resulting from scattering of the laser beam of the absorption wavelength λ1 by dust in the gas or by the gas itself is detected by a photodetector provided near the laser emitter. In this case, a time of detecting the scattered light by the photodetector differs according to a distance between the laser emitter and a position at which the laser beam is scattered. By converting this time property to a distance property, a detection signal of scattered light from a desired section is obtained. Based on the obtained detection signal, an attenuation rate of light of the wavelength λ1 in the section with respect to the laser beam emitting is calculated.
Likewise, laser beam having a non-absorption wavelength λ2 of the target component is emitted from the laser emitter to the same remotely-located gas, to calculate an attenuation rate of light of the wavelength λ2 in the same section.
A light attenuation rate by the target component can be obtained based on the attenuation rate of light of the wavelength λ1 in the section and the attenuation rate of light of the wavelength λ2 in the section. Further, the concentration of the target component in the section can be determined from the obtained attenuation rate and known reference data.
Note that Patent Documents 1 and 2 are listed below as prior art documents of this application.    [Patent Document 1] Japanese Patent No. 3861059    [Patent Document 2] Japanese Patent No. 3699682
In the case of detecting the concentration of the target component in the gas in the above-mentioned manner, a very expensive apparatus needs to be used for the following reason.
The light scattered by the dust in the gas or by the gas itself has a very low intensity. Accordingly, it is necessary to use a laser emitter capable of emitting laser beam of a sufficiently high intensity so that the photodetector can detect the scattered light.
However, particularly when emitting the laser beam outdoors, there is a laser intensity constraint for safety reasons. To make up for such a laser intensity, a large, difficult-to-handle, and expensive light collector or the like needs to be used in order to detect weak scattered light.